The present invention relates to a resin composition for a color filter, and more particularly to a resin composition which can realize a liquid crystal display device having excellent display quality.
In recent years, color liquid crystal display devices have drawn attention as flat displays. One example of the color liquid crystal display devices is a transmission liquid crystal display device such that a color filter comprising a black matrix, a colored layer of a plurality of colors (in general, the three primary colors of red (R), green (G), and blue (B)), a common transparent electrode layer, and an aligning layer is provided so as to face a counter electrode substrate comprising a thin film transistor (a TFT device), an pixel electrode, and an aligning layer, while leaving a predetermined gap between the color filter and the counter electrode substrate, and a liquid crystal material is poured into the gap to form a liquid crystal layer. Another example of the color liquid crystal display devices is a reflection liquid crystal display device wherein, in the above color filter, a reflective layer is provided between the substrate and the colored layer.
In these color liquid crystal display devices, a change in the state of alignment of the liquid crystal caused, for example, by an alignment failure of the liquid crystal, a change in voltage applied to the liquid crystal, and a variation in voltage within the display surface, results in the occurrence of display failures (unacceptable display phenomena) which are classified into sticking and uneven whiteness.
Sticking is a phenomenon such that, when a voltage has been applied to an identical pixel for a given period of time followed by a lowering in voltage or the stop of the application of the voltage, the transmittance of this pixel becomes different from the transmittance of pixels, located around this pixel, to which the voltage has not been applied for the given period of time, and, as a result, an uneven display is visually perceived and is continued even after standing for a long period time. In the sticking phenomenon of normally white panels, the pixel, to which a voltage has been applied for a given period of time, is seen more darkly than pixels located around this pixel. This sticking phenomenon is attributable to the fact that an ionic material is deposited on an electrode during the application of the voltage and, after the stop of the application of the voltage, remains adsorbed on the electrode and, as a result, the voltage derived from the ionic material continues to act on the liquid crystal.
On the other hand, uneven whiteness is a phenomenon such that an uneven display is visually perceived due to the fact that, when a voltage is applied to display a black screen, the transmittance does not become zero in a part of the display region. The cause of this phenomenon is considered as follows. Although the voltage applied across the electrodes should be kept constant, when an ionic material is present in the liquid crystal, this ionic material is moved, that is, a current flows, resulting in a drop of voltage across the electrodes.
Techniques which have taken the above display failure phenomena into consideration include a technique relating to ionic impurities contained in a material composition for liquid crystal devices (Japanese Patent Laid-Open No. 254918/1989), a technique relating to chloride ions and nitrate ions contained in a material composition for liquid crystal devices (Japanese Patent Laid-Open No. 64619/1999), and a technique relating to the amount of water generated from color filters (Japanese Patent Laid-Open No. 133223/1999).
In the prior art techniques, however, target ionic impurities and constituent materials are limited. This poses a problem that the presence of impurities other than the target impurities and the inclusion of impurities in constituent materials other than the target constituent materials result in display failures of color liquid crystal display devices. Further, in the resin composition used in the production of color filters, the kind and amount of impurities vary depending, for example, upon the kind of constituent materials, manufacturers, and names of articles. This has made it difficult to predict the influence of a change in constituent materials on display characteristics of color liquid crystal display devices. Further, it is difficult to specify all of materials causative of display failure phenomena of color liquid crystal display devices. Even though all the materials causative of display failure phenomena have been specified, the range of usable constituent materials is unfavorably significantly narrowed when a resin composition free from any causative material is to be used as the constituent material. Further, in this case, the production cost of the resin composition is increased.
Under these circumstances, the present invention has been made, and it is an object of the present invention to provide a resin composition for a color filter, which can surely prevent the occurrence of display failure phenomena of color liquid crystal display devices, can broaden the range of selection of usable constituent materials, and does not incur increased cost.
The present inventors have considered that a resin member for constituting a color filter in contact with a liquid crystal layer in a liquid crystal display device is one of sources for the above-described ionic materials and have directed attention, as properties having a correlation with display failures caused by ionic materials which have migrated from the resin member into the liquid crystal layer, to voltage retention and residual DC (xcex94E) of a liquid crystal after the extraction of impurities from components constituting a resin composition for a resin member.
In order to attain the above object, according to one aspect of the present invention, there is provided a resin composition for a color filter, comprising a combination of a volatile component with a nonvolatile component, wherein:
not less than 50% by weight of the nonvolatile component is accounted for by a first constituent, which, after the impurity extraction of a liquid crystal, permits the liquid crystal to have a voltage retention of not less than 60% and to have a residual DC (xcex94E) of not more than 0.6 V; and
when less than 50% by weight of the nonvolatile component is accounted for by a second constituent, which, after the impurity extraction of a liquid crystal, cannot permit the liquid crystal to have a voltage retention of not less than 60% and to have a residual DC (xcex94E) of not more than 0.6 V, a requirement represented by formula (1) for the relation between the content of the second constituent and the voltage retention and a requirement represented by formula (2) for the relation between the content of the second constituent and the residual DC are satisfied:
Content (wt %)÷voltage retention (%) less than 0.1xe2x80x83xe2x80x83(1)
Content (wt %)xc3x97residual DC (V) less than 5xe2x80x83xe2x80x83(2).
According to a preferred embodiment of the resin composition for a color filter according to the present invention, a photoreactive compound as a sublimable component is further contained in the resin composition.
Further, according to a preferred embodiment of the resin composition for a color filter according to the present invention, the nonvolatile component comprises at least one member selected from a pigment, a pigment derivative, and a surfactant.